#include <stdio.h>
#include <math.h>

typedef struct {
  double  x; /* x座標 */
  double  y; /* y座標 */
} Point;

Point rotate1(double, Point, Point);
void  rotate2(double, Point *, Point *);

int main()
{
  double rad, deg;
  Point c = {1.0, 1.0}, a = {2.0, 3.0}; /* 中心と回転対象の点 */
  Point b1, b2;         /* 結果を入れる構造体 */
  
  printf("回転角 [度] を入力してください\n");
  scanf("%lf", &deg);
  rad = deg*M_PI/180;
  printf("回転角 %f [deg] (%f [rad])\n", deg, rad);
  
  /* 関数呼び出しおよび関連するコード */
  b1 = rotate1(rad, c, a);
  b2 = a;
  rotate2(rad, &c, &b2);

  printf("Center  : %f %f\n", c.x, c.y);
  printf("Point A : %f %f\n", a.x, a.y);
  printf("Point B (rotate1) : %f %f\n", b1.x, b1.y);   /* rotate1関数の結果を出力 */
  printf("Point B (rotate2) : %f %f\n", b2.x, b2.y);   /* rotate2関数の結果を出力 */
  return 0;
}

Point rotate1(double rad, Point center, Point p)
{
  double dx, dy;
  Point pnew;

  dx = p.x - center.x;
  dy = p.y - center.y;
  pnew.x = dx*cos(rad) + dy*(-sin(rad)) + center.x;
  pnew.y = dx*sin(rad) + dy*cos(rad) + center.y;
  return pnew;
}

void rotate2(double rad, Point *center, Point *p)
{
  double dx, dy;

  dx = p->x - center->x;
  dy = p->y - center->y;
  p->x = dx*cos(rad) + dy*(-sin(rad)) + center->x;
  p->y = dx*sin(rad) + dy*cos(rad) + center->y;
}